Sorry, cod's off. And with stocks of other staples also creaking under pressure, fish-eaters are being encouraged to sample unfamiliar alternatives. Is there an appetite for these monsters from the deep?

Even the humble fishfinger has got a little more exotic. Instead of flakes of the expected cod, the crumbed morsels are more likely to contain hoki, a white-fleshed fish sourced from abundant stocks at the opposite end of the Earth.

Birds Eye Walls introduced the New Zealand fish two years ago in line with the policy of its parent company, Unilever, to use only fish from sustainable stocks by 2005.

But now this ethical stance - which also makes good business sense as emptied waters means no fish products to sell - is proving harder to stick to than the multinational planned. On Monday, Unilever published a report which said: "We are unlikely to hit our 2005 target in the UK, although we have made progress towards it."

The greyish flesh of rat-tails was used in 60s fishfingers [FAO image]

Just 6% of its global catch came from certified sustainable stocks at the end of last year. But overall, one-third came from sources the company judged to be sustainable, says spokesman Trevor Gorin.

Not only is it a drawn-out process certifying fisheries - currently only six worldwide have made the grade - customers are still reluctant to buy unfamiliar fish and instead plump for the old favourites cod and haddock. Yet these are fish which have been intensively fished to the point of crisis.

Old habits die hard

Cod, which thrives in the cold, deep waters of the North Sea, has long been a popular dish. Archaeological digs show that Britons have eaten this fish for 7,000 years.

FISH OF THE DAY

Fish consumption has risen 240% since 1960

From 1960 to 1996, production for human consumption up from 27m to 91m tonnes

Demand in 2010 is projected to reach 120m tonnes

Figures from World Resources Institute and Food and Agriculture Organisation

Today, polls show that despite warnings that cod stocks are on the verge of collapse, it accounts for more than one-third of household purchases and last year restaurants served 136m cod meals.

But cod is not the only fish in the sea. There are enough species caught around the UK for a fish-eater to have a different dish each week of the year. A single haul can include up to 20 different species, many not recognised as being local but which may be familiar to those who holiday in the Mediterranean.

Marine conservationists want us to rediscover a taste for these local delights, which include pilchards - or Cornish sardines, as West Country fisherfolk have rebranded the maligned species - and Thames herrings. Other alternatives include pollack, megrim, huss and mahi-mahi - which tastes not dissimilar to the under-threat swordfish.

WWF - which last year helped publish a Good Fish Guide listing endangered species - hopes that if we start buying by-catch, such as dab, this would reduce the wastage associated with discarding less profitable species.

Treasures of the deep

The hunt for sustainable alternatives does have its pitfalls. By going to New Zealand for hoki or Alaska for pollack or South Africa for hake, we could just be exporting the problem of over-fishing further around the planet.

Dr Keith Duff, chief scientist at English Nature, says although he hopes other food suppliers will follow Unilever's lead in trying to find other sources of tasty fish, there's a danger of repeating mistakes already made with cod and haddock. "We need to change the approach to fishing management, including quotas, to make sure we leave enough fish in the sea for them to survive and thrive."

Don't develop a taste for at-risk fish such as orange roughy [FAO image]

And sometimes fish we develop a taste for turn out not to be as abundant as originally thought, says Oliver Crimmen, the fish curator at London's Natural History Museum.

"Orange roughy, for instance, was rapidly fished out as it turned out that it only lived in the places it was first found."

Going deeper isn't the answer either. Fish from the mid-depths such as sea bass, monkfish and some types of tuna are now endangered. The prized Patagonian toothfish - on the menu at fashionable eateries in Tokyo, London and New York - is now virtually worth its weight in gold it is so scarce.

"True deep-water fish are inedible," says Mr Crimmen. "The pressure is so great at the bottom of the sea, they've evolved so as not to be crushed. These fish are either small and very bony, or have watery flesh and thin bones - they don't have nice beefy muscles you can sink your teeth into."

The lessons of over-fishing are there in history. Herring was once so popular that stocks collapsed in the 1970s and have only now recovered enough to allow controlled fishing. And 11 years ago in Canada, one of the world's most abundant populations of cod went into freefall, resulting in a total fishing ban and 40,000 lost jobs.

Nor is it a recent problem. There is a reference to depleted stocks in Journal Of A Voyage To Lisbon, written by Henry Fielding in 1756.

"There's plenty of examples of species pushed to the brink by over-fishing, but none yet have become extinct," says Mr Crimmen. "We shouldn't wait until that happens to take action."